Lighting systems for indoor and outdoor illumination of advertising signs and for other purposes have been used for many decades. An illumination system may include several gas discharge tubes, such as cold cathode tubes or fluorescent tubes. A cold cathode tube is a sealed glass tube that is filled with inert gas, such as argon or neon, wherein different ionized gases provide light of different colors. A fluorescent tube is a sealed glass tube having its inner walls coated with phosphorus and the tube is filled with, e.g., mercury vapor. Both types of tubes may be fabricated in many different shapes and sizes. The tubes include electrodes connected to a high-frequency, high-voltage power supply that provides a striking voltage and a running voltage. The gas inside the tubes is ionized so that the gas atoms or molecules are stimulated to emit light of a known wavelength. To ionize the inert gas, a striking voltage of approximately 1.5 times the running voltage is required. Once ionized, a constant current is preferably maintained across the gas tube at a running voltage. The striking and running voltages are proportional to the tube length and are typically in the range of several hundred to several thousand Volts. The luminous intensity of the ionized gas is proportional to the current that flows between the electrodes inside the tube.
For advertizing purposes, each gas discharge tube may be located within a letter enclosure. The letter enclosure may be shaped in the form of a letter or may have a rectangular shape with a letter sign in front of the gas discharge tube. The effectiveness of an advertising sign also depends on having letters of various shapes and sizes emitting light of a selected intensity, which is usually equal for all letters. Typically, the individual gas discharge tubes are powered by high-frequency, high-voltage power supplies. The output from each power supply is connected to the tube electrodes using high-voltage GTO cables. These high-voltage cables require special installation and can have only a limited length due to safety requirements. To install an outside sign, each letter may require two GTO cables located in two separate and relatively large holes drilled through an external wall. Thus, installing a large number of letters or symbols may require a significant amount of time and possibly damage to the wall.
There is still a need for an illumination system that includes several gas discharge tubes, is easy to install and operates efficiently.